Recently cold cathode devices are getting attention as an electron beam source. In the cold cathode a microprocessing technology is required to increase field intensity. As materials for the cold cathode, Si, to which microprocessing may be applied, and metals with high melting points such as W and Mo, which are heat resistant, have been used, but diamond cold cathodes are getting attention because it has negative electron-affinity.
Various forms have been proposed for the diamond cold cathode. For example, there are a pn junction type described in the publication WO93/15522, and a metal cathode coated with diamond described in Journal of Vacuum Science and Technology B14 (1996) 2050. In the pn junction type, as shown in FIG. 5, an n-type diamond 51 is layered on a p-type diamond 52, and an electrode 50 is disposed on the n-type diamond 51, wherein bias voltage is applied to the electrode to emit electron. Further, as shown in FIG. 6, sharpened diamond cathodes are proposed in Japanese Laid Open Patent Publication No. Hei 8-264111 and the publication WO98/44529, wherein a diamond 60 is formed in a Si mold 61.